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4nec2 hidden variables.
Am trying to run an optimization on my 3 element yagi which I finally
got into the editor, which was difficult enough. The optimizer says: no variables selected but there are none to select. Empty list field. Oh, how I hate this. Praise Bill Gates for his user-friendly WINDOWS and to hell with all amateur softwares. Nowhere in the helps and getting started they explain that. I do not want to learn from examples, I rather work from the basics upwards. Would anyone learn math from a calculus formula without knowing the arabic numbers first? Am in a baad mood tooday. w. |
4nec2 hidden variables.
On Sat, 13 Aug 2011 21:07:17 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: Am trying to run an optimization on my 3 element yagi which I finally got into the editor, which was difficult enough. The optimizer says: no variables selected but there are none to select. Empty list field. I have no experience with 4nec2 to speak of, but what it sounds like is for an optimizer to work, you must first describe (name as a variable) what characteristic you would like to vary until the optimizer achieved an optimal result. One guess for a three element yagi, I would suspect you would name three variables, the elements, changing each by by an incremental length (another variable) at a fixed frequency (another variable) for maximum gain (another variable) in a particular direction (another variable). Having said that little at seven variables (some fixed in value), it is quite a page full of algebra stated in a formulaic way for the optimizer (However, I fully expect that would be in a table description, not a literal formula). Having said even that little, it lends a peek into the number of all the combinations and permutations of design this leads to. Each variable taken individually against all the possible others - and then repeated for the others in turn - leads to what mathematicians call Combinatorial Explosion (you don't have enough time to wait for the best solution). This is where constraints are added to the algebra, and you offer "close enough" as one of them to limit testing. Nowhere in the helps and getting started they explain that. I do not want to learn from examples, I rather work from the basics upwards. Would anyone learn math from a calculus formula without knowing the arabic numbers first? Proving the validity of numbers consumed a volume of proofs back when Whitehead and Russell wrote "Principia Mathematica." It was logically dead on arrival BEFORE it was published - and yet it was the best description of simple math known. Calculus was simpler as it is principally symbol dominated. 73's Richard Clark, KB7QHC |
4nec2 hidden variables.
Would anyone learn math from a calculus
formula without knowing the arabic numbers first? Proving the validity of numbers consumed a volume of proofs back when Whitehead and Russell wrote "Principia Mathematica." "From this proposition it will follow, when arithmetical addition has been defined, that 1+1=2." Volume I, 1st edition, page 379 73's Richard Clark, KB7QHC |
4nec2 hidden variables.
On Sat, 13 Aug 2011 21:07:17 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: Am trying to run an optimization on my 3 element yagi which I finally got into the editor, which was difficult enough. The optimizer says: no variables selected but there are none to select. Empty list field. Are you using symbols, or did you hard code all the dimentions in ft or meters? The optimizer won't work without using symbols. 4NEC2 forums. Where to ask such questions: http://fornectoo.freeforums.org Oh, how I hate this. If it were easy, it would not be fun. One must suffer before enlightenment. Praise Bill Gates for his user-friendly WINDOWS and to hell with all amateur softwares. If you were around in the bad old days of computing, you might be praising Bill Gates for saving us from the evils of big computer companies. There was a time when you had to buy pre-formatted floppies to work in DEC PC's, and when every machine had a different floppy disk format. Anyway, your frustration with not reading the manual and learning to use 4NEC2 has nothing to do with Windoze or Bill Gates. Nowhere in the helps and getting started they explain that. True. Found with Google in a few minutes: 4NEC2 tutorial including optimizer and evolver: http://heplx3.phsx.ku.edu/~dzb/antcal/nec-files/_GetStarted.txt See section 5. Video of optimizer (25 min): http://www.youtube.com/watch?v=kYy6Yur127A I do not want to learn from examples, Then you will fail or at least be more frustrated. Hacking your own path throught the wilderness is far more work than following in someone elses footsteps. I rather work from the basics upwards. Would anyone learn math from a calculus formula without knowing the arabic numbers first? Most certainly possible. There are numerous tools the devices that I use with only a minimal understanding for how they work. For example, there are many drivers on the road that could not even begin to explain how a gasoline engine works. (Hint: Carnot heat engine). I suspect that such basic knowledge would not improve their driving ability. Am in a baad mood tooday. Have a better day. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
On Sat, 13 Aug 2011 14:15:22 -0700, Jeff Liebermann
wrote: .......... I am making progress, though. Got the optimizer running and edited a few of the example files to have the variables selection available. Works. Now I watch the optimizer quickly de-optimizing the antennas until they radiate into the wrong direction or get stuck in a circular radiation diagram. In one case the optimizer bent and rotated the dipoles around, I bet no specialist can do what I can. Real fun, that is :-) Video of optimizer (25 min): http://www.youtube.com/watch?v=kYy6Yur127A Yeah, thats good. Sitting back and watch. Thanks for the idea of watching the Youtube demos. Better than endless trial-and-error. My goal is to find out what makes a direction finding antenna different from a gain optimized antenna. F/B ratio is all that matters for ARDF, for example. Gain is secondary and side-lobes should be absent. I must get that NEC working by all means. Regards, w. |
4nec2 hidden variables.
On Sun, 14 Aug 2011 00:59:40 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: My goal is to find out what makes a direction finding antenna different from a gain optimized antenna. That's easy (having helped design 2 commercial direction finders). Low side lobes and good front to back. Gain is well down the list of requirements. Side lobes will drive any direction finding scheme towards insane results by generating false peaks in the direction. The ability to recognize these is a function of how much time you want to put into the software. Reflections will also cause problems, but more so with side lobes. To prove a point, I once threw together a rotating antenna direction finder using a low gain directional antenna (but with low side lobes, and no rear lobe). Due to the low gain, the -3dB beam width was a rather wide 60 degrees. I rotated the antenna slowly, and the computah made lots of signal level measurements. The result was that I could determine the direction within about +/-2degrees. Of course a higher gain antenna would resolve the signal direction much better, and could probably be rotated faster, but all would be much larger. However, there's a problem. High gain antennas tend to have boresight errors. Small asymmetries, such as mountings, gamma matches, and baluns, will have an effect. F/B ratio is all that matters for ARDF, for example. F/B could be considered a side lobe at 180 degrees. Like other side lobes, it needs to be minimized. Gain is secondary and side-lobes should be absent. Absent is difficult. Minimized might be a better goal. With a log amp driving the signal level measuring device, three orders of magnitude should be sufficient. I must get that NEC working by all means. Slow down. Such things take time. What manner of direction finder are you building and what frequency? Doppler? Rotating antenna? Phasing? Time difference of arrival? Homer? Adcock? Ouija board? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
On Sat, 13 Aug 2011 14:15:22 -0700, Jeff Liebermann
wrote: Am in a baad mood tooday. Have a better day. Sorry, bad mood again. Watched the tutorials on Youtube. Remarkably he starts loading an antenna and then deleting the elements to get a blank builder screen. The 4nec2 cannot start with a "new" file, it must load something from before. Only then I may select NEW. This is a bug. I copied the moves from the tutorial on my NEW antenna, and I cannot place a source on the dipole. Does not work. No error message, nothing. So I will load some old antenna, delete everything and try again as shown in the tutorial. Within 5 minutes of work I have a list of 5 errors, program errors, repectively bugs, mis-leading the user. Can't type as fast as the bugs occur, I just described only one. Of course I have no right to complain because it's free. Yeah. w. |
4nec2 hidden variables.
On Sun, 14 Aug 2011 22:02:32 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: On Sat, 13 Aug 2011 14:15:22 -0700, Jeff Liebermann wrote: Am in a baad mood tooday. Have a better day. Sorry, bad mood again. Watched the tutorials on Youtube. Remarkably he starts loading an antenna and then deleting the elements to get a blank builder screen. The 4nec2 cannot start with a "new" file, it must load something from before. Only then I may select NEW. This is a bug. I copied the moves from the tutorial on my NEW antenna, and I cannot place a source on the dipole. Does not work. No error message, nothing. So I will load some old antenna, delete everything and try again as shown in the tutorial. Within 5 minutes of work I have a list of 5 errors, program errors, repectively bugs, mis-leading the user. Can't type as fast as the bugs occur, I just described only one. Of course I have no right to complain because it's free. Yeah. w. Now I watched the tutorial again and again http://www.youtube.com/watch?v=3AqMq0J3WBc and after 14:11 he adds a voltage source. He does a horizontal movement with the cursor on the dipole wire and only then the 4nec2 will place the voltage source on the dipole. He does not mention that or explain that move. This stupid bug -and a program bug that is, and a large one- this stupid bug has cost me 2 hours of struggling. Ready for the next bug. w. |
4nec2 hidden variables.
On Sun, 14 Aug 2011 22:24:29 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: ......... This stupid bug -and a program bug that is, and a large one- this stupid bug has cost me 2 hours of struggling. Ready for the next bug. Want one? 4nec2 from time to time destroys it's saved antenna files. Just lost another 2 hours of work. Now I understand why it's free. Can't charge money for bugs. w. |
4nec2 hidden variables.
On Sun, 14 Aug 2011 22:02:32 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: On Sat, 13 Aug 2011 14:15:22 -0700, Jeff Liebermann wrote: Sorry, bad mood again. Like I said. One must suffer before enlightenment. Watched the tutorials on Youtube. Remarkably he starts loading an antenna and then deleting the elements to get a blank builder screen. The 4nec2 cannot start with a "new" file, it must load something from before. Only then I may select NEW. This is a bug. Well, there is no "new" button or choice under "File". Ask Arie Voors for the feature. It seems easy enough to add to the program. I copied the moves from the tutorial on my NEW antenna, and I cannot place a source on the dipole. Does not work. No error message, nothing. So I will load some old antenna, delete everything and try again as shown in the tutorial. Well, I've never had that problem because I don't try to "paint" the antenna using the isometric or 3D views. It's not accurate enough unless you snap to a grid. I create the antenna either externally, with a text editor, or using the spreadsheet style editor. I import that into 4NEC2 and make any necessary changes (and fix any screwups). For geometric shapes, I use the external shape generator, which will do surfaces, parabolic dishes, etc. 4NEC2 is not a drawing program. Within 5 minutes of work I have a list of 5 errors, program errors, repectively bugs, mis-leading the user. Impressive. You might want to search the 4NEC2 forums to see if any of them have been previously reported. http://fornectoo.freeforums.org Note that there is a section specifically for requesting new features. Can't type as fast as the bugs occur, I just described only one. Of course I have no right to complain because it's free. In my limited experience, people complain more about free software than paid software. That's usually because the author(s) encourage feedback in order to improve their product. Yeah. Thanks for ignoring my questions. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
On Sun, 14 Aug 2011 23:27:33 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: Want one? Not really, since I can't do anything to fix the alleged problem. 4nec2 from time to time destroys it's saved antenna files. Just lost another 2 hours of work. Nobody does backups until after they have lost data. I've been using 4NEC2 for at least 7 years and have never lost a file. Well, I have accidentally overwritten a file, but that was my fault. When I tinker with antennas, I save multiple versions of the same design with the version number appended as in file001.nec. This way, if I make a horrible mistake, I can go back to a previous version and try again. Now I understand why it's free. Can't charge money for bugs. Well, that why we have alternatives to 4NEC2 and why I don't charge for my free advice: http://www.smeter.net/antennas/mmana.php http://www.eznec.com http://www.nittany-scientific.com http://www.hamradiosecrets.com/antenna-design-software.html http://www.si-list.net/swindex.html (old but still useful) -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
On Sun, 14 Aug 2011 19:46:34 -0700, Jeff Liebermann
wrote: On Sun, 14 Aug 2011 23:27:33 +0200, Helmut Wabnig [email protected] --- -.dotat wrote: Want one? Not really, since I can't do anything to fix the alleged problem. 4nec2 from time to time destroys it's saved antenna files. Just lost another 2 hours of work. Nobody does backups until after they have lost data. I've been using 4NEC2 for at least 7 years and have never lost a file. Well, I have accidentally overwritten a file, but that was my fault. When I tinker with antennas, I save multiple versions of the same design with the version number appended as in file001.nec. This way, if I make a horrible mistake, I can go back to a previous version and try again. Now I understand why it's free. Can't charge money for bugs. Well, that why we have alternatives to 4NEC2 and why I don't charge for my free advice: http://www.smeter.net/antennas/mmana.php http://www.eznec.com http://www.nittany-scientific.com http://www.hamradiosecrets.com/antenna-design-software.html http://www.si-list.net/swindex.html (old but still useful) ###########"Backup, you say it". ########### When optimizing for F/B also 4nec2 results in a too short driven element, same as YAGICAD, they obviously use the same formula, (a long two-liner) from literature. I actually built antennas following that prescription, and they do not work without additional corrections, e.g. a very long hair-pin match. Imagine a 3 element 2 meter yagi, | | | | | | | | | | | | | | | | | | | | | Something is wrong here with the capacitive driven element. Now I am having a hard time, because I want to find out in what differs a gain optimized vs a F/B optimized antenna and it is questionable whether that can be done with software. Have not tried other programs yet. http://imageshack.us/photo/my-images/837/snc14096a.jpg/ The Front to Back ratio is very frequency dependent http://imageshack.us/photo/my-images/220/fbratio.jpg/ (Without the hair pin match) http://img5.imageshack.us/img5/3479/snc14112hairpin.jpg Therefore I put the driver on a slider http://img841.imageshack.us/img841/8...14097small.jpg which allows to adjust the working frequency of the antenna over a 10 MHz range on 2 meters. Adjust for minimum reception from the back and the antenna is optimized for that frequency. Now I want to collect a list of recipes which allow to build the antenna without having to tweak it on the antenna analyzer. A similar design once was offered by DIAMOND MAY1000 http://www.rfparts.com/diamond/MAY1000.html Look at the frequency chart http://www.rfparts.com/diamond/pdfdo...dj%20Chart.pdf With that antenna one could adjust the element lengths *and* the distance between the elements, which is crucial for the F/B ratio. A Yagi with fixed element positions can only be used for 1 frequency (within a very small range) and therefore may be impractical in many situations. The CEBIK tape measure antenna with their water-pipe construction could be easily modified with a moveable center element. http://www.g6hoq.com/documents/2m%20...structions.pdf Above line as shortlink: http://tinyurl.com/3m5p5nq w. |
4nec2 hidden variables.
Helmut, your ranting and raving about 4Nec2 seem entirely unfair, the 'bugs' that you complain do not seem to be bugs at all, just the way the program works; which is not to your liking. Placing sources requires that you click whilst away from the wire and then drag the source onto the wire. This is not a bug, just the way that the author chose to do it. In many years of using 4Nec2 I have never had it loose a file, so I can only assume that there is some sort of problem at your end. Yes, it would be nice to have a 'New' button, but again not a bug, just the way that the program works. If this minor inconvenience pains you that much ask the author to add one. Regarding optimization the phrase 'garbage in garbage out' springs to mind. Optimizers are just that, optimizers, they WILL NOT take a rubbish design and turn it into the perfect antenna. Optimizers rely on finding minima (or maxima) in the set of parameters that you supply, so unless you are close to a good design it is very likely that they will 'get stuck' in a local minima and then home in on something other than an optimum design. So you have to have a good design to start with and also not try to optimize to a set of unrealistic goals. This applies TO ALL optimizers not just 4Nec2. Regards Jeff |
4nec2 hidden variables.
So, the software is not perfect... but some of your complaints are are
result of your own ignorance of modelling, NEC and 4NEC2. Helmut, your vitrolic rant doesn't strike a chord with me. Right now, Arie has some personal issues that we would all rather not have in our lives, and yet he is finding time for some problem resolution. Arie, I dips me lid (that means "hats off" in Oz). Owen |
4nec2 hidden variables.
On Mon, 15 Aug 2011 09:59:00 +0100, Jeff wrote:
Placing sources requires that you click whilst away from the wire and then drag the source onto the wire. This is not a bug, just the way that the author chose to do it. Show me the place in the manual or help where that is described. Normally we do drag and drop, but here we must drag, drop & move. Made me crazy, but no longer now since I know it, and I will keep it a secret and not tell anyone. In many years of using 4Nec2 I have never had it loose a file, so I can only assume that there is some sort of problem at your end. Of course, it's free, so it must be my fault. From the little programming I did, I know it's 99% user interface and 1% programming the more interesting part. Yes, it would be nice to have a 'New' button, but again not a bug, just the way that the program works. If this minor inconvenience pains you that much ask the author to add one. No, no, it's free. Regarding optimization the phrase 'garbage in garbage out' springs to mind. Optimizers are just that, optimizers, they WILL NOT take a rubbish design and turn it into the perfect antenna. Optimizers rely on finding minima (or maxima) in the set of parameters that you supply, so unless you are close to a good design it is very likely that they will 'get stuck' in a local minima and then home in on something other than an optimum design. So you have to have a good design to start with and also not try to optimize to a set of unrealistic goals. This applies TO ALL optimizers not just 4Nec2. Regards Jeff You are right, that's how it is. w. |
4nec2 hidden variables.
On 15/08/2011 13:50, Helmut Wabnig wrote:
On Mon, 15 Aug 2011 09:59:00 +0100, wrote: Placing sources requires that you click whilst away from the wire and then drag the source onto the wire. This is not a bug, just the way that the author chose to do it. Show me the place in the manual or help where that is described. Normally we do drag and drop, but here we must . Made me crazy, but no longer now since I know it, and I will keep it a secret and not tell anyone. Firstly it is not 'drag, drop& move'; it is click, drag & drop! Try reading the Help a little more closely, you will find that it says: "The next thing to do is add a voltage-source. While still in Add-mode, click the 'Source button' (right of the 'Wire button'). Next click and hold down your left mouse-button somewhere in the picture-box. At the current mouse-pointer position a new source-object is displayed. Drag the source-object to the middle of the second wire, just between the two lower wires-ends of the feedline and release the mouse-button. When properly positioned a new source is now added." In many years of using 4Nec2 I have never had it loose a file, so I can only assume that there is some sort of problem at your end. Of course, it's free, so it must be my fault. From the little programming I did, I know it's 99% user interface and 1% programming the more interesting part. No one else reports this problem so draw your own conclusions!!! The fact that it is free has no bearing on it. Yes, it would be nice to have a 'New' button, but again not a bug, just the way that the program works. If this minor inconvenience pains you that much ask the author to add one. No, no, it's free. Have you contacted the author and asked for this feature? No? I thought not. Again the fact that it is free has no bearing. Regarding optimization the phrase 'garbage in garbage out' springs to mind. Optimizers are just that, optimizers, they WILL NOT take a rubbish design and turn it into the perfect antenna. Optimizers rely on finding minima (or maxima) in the set of parameters that you supply, so unless you are close to a good design it is very likely that they will 'get stuck' in a local minima and then home in on something other than an optimum design. So you have to have a good design to start with and also not try to optimize to a set of unrealistic goals. This applies TO ALL optimizers not just 4Nec2. Regards Jeff You are right, that's how it is. Yes that is the way it is with ALL optimizers, not just 4nec2; gigo. No one is forcing you to use 4nec2, however, no one else seems to be having the problems that you claim are 'bugs', perhaps you should have more patience, read the help more closely, and not be so quick to criticize. Jeff |
4nec2 hidden variables.
On Mon, 15 Aug 2011 14:20:28 +0100, Jeff wrote:
On 15/08/2011 13:50, Helmut Wabnig wrote: On Mon, 15 Aug 2011 09:59:00 +0100, wrote: Placing sources requires that you click whilst away from the wire and then drag the source onto the wire. This is not a bug, just the way that the author chose to do it. Show me the place in the manual or help where that is described. Normally we do drag and drop, but here we must . Made me crazy, but no longer now since I know it, and I will keep it a secret and not tell anyone. Firstly it is not 'drag, drop& move'; it is click, drag & drop! Try reading the Help a little more closely, you will find that it says: "The next thing to do is add a voltage-source. While still in Add-mode, click the 'Source button' (right of the 'Wire button'). Next click and hold down your left mouse-button somewhere in the picture-box. At the current mouse-pointer position a new source-object is displayed. Drag the source-object to the middle of the second wire, just between the two lower wires-ends of the feedline and release the mouse-button. When properly positioned a new source is now added." It does not work as described, period. w. |
4nec2 hidden variables.
On Mon, 15 Aug 2011 14:20:28 +0100, Jeff wrote:
On 15/08/2011 13:50, Helmut Wabnig wrote: On Mon, 15 Aug 2011 09:59:00 +0100, wrote: Placing sources requires that you click whilst away from the wire and then drag the source onto the wire. This is not a bug, just the way that the author chose to do it. Show me the place in the manual or help where that is described. Normally we do drag and drop, but here we must . Made me crazy, but no longer now since I know it, and I will keep it a secret and not tell anyone. Firstly it is not 'drag, drop& move'; it is click, drag & drop! Try reading the Help a little more closely, you will find that it says: "The next thing to do is add a voltage-source. While still in Add-mode, click the 'Source button' (right of the 'Wire button'). Next click and hold down your left mouse-button somewhere in the picture-box. At the current mouse-pointer position a new source-object is displayed. Drag the source-object to the middle of the second wire, just between the two lower wires-ends of the feedline and release the mouse-button. When properly positioned a new source is now added." It does not work as described, when inserting a source on a dipole wire in the center segment, one of the first things to do in Example1. w. |
4nec2 hidden variables.
Firstly it is not 'drag, drop& move'; it is click, drag& drop! Try reading the Help a little more closely, you will find that it says: "The next thing to do is add a voltage-source. While still in Add-mode, click the 'Source button' (right of the 'Wire button'). Next click and hold down your left mouse-button somewhere in the picture-box. At the current mouse-pointer position a new source-object is displayed. Drag the source-object to the middle of the second wire, just between the two lower wires-ends of the feedline and release the mouse-button. When properly positioned a new source is now added." It does not work as described, when inserting a source on a dipole wire in the center segment, one of the first things to do in Example1. w. Utter Rubbish!!! It works EXACTLY as described!!! Hold down the left mouse button, drag the source to the segment where you wish it to be, release the button - exactly as described!!! Jeff |
4nec2 hidden variables.
On 8/13/2011 12:07 PM, Helmut Wabnig wrote:
Am trying to run an optimization on my 3 element yagi which I finally got into the editor, which was difficult enough. The optimizer says: no variables selected but there are none to select. Empty list field. Oh, how I hate this. Praise Bill Gates for his user-friendly WINDOWS and to hell with all amateur softwares. Nowhere in the helps and getting started they explain that. I do not want to learn from examples, I rather work from the basics upwards. Would anyone learn math from a calculus formula without knowing the arabic numbers first? Am in a baad mood tooday. w. Does your model have symbols defined (using the 4nec2 specific SY card?) That's what it uses to populate the list. Which editor are you using? If you already have a NEC input deck, it's easiest to use the non-graphical editor. What are you optimizing for. Sure, you can whine about wanting better help files, but face it, Arie is providing the product for free. If you are already proficient in NEC, the help provided is fairly useful. If you are learning if from scratch, yep, it's a pain. |
4nec2 hidden variables.
On 8/13/2011 3:59 PM, Helmut Wabnig wrote:
On Sat, 13 Aug 2011 14:15:22 -0700, Jeff wrote: .......... I am making progress, though. Got the optimizer running and edited a few of the example files to have the variables selection available. Works. Now I watch the optimizer quickly de-optimizing the antennas until they radiate into the wrong direction or get stuck in a circular radiation diagram. In one case the optimizer bent and rotated the dipoles around, I bet no specialist can do what I can. Real fun, that is :-) Video of optimizer (25 min): http://www.youtube.com/watch?v=kYy6Yur127A Yeah, thats good. Sitting back and watch. Thanks for the idea of watching the Youtube demos. Better than endless trial-and-error. My goal is to find out what makes a direction finding antenna different from a gain optimized antenna. F/B ratio is all that matters for ARDF, for example. Gain is secondary and side-lobes should be absent. I must get that NEC working by all means. Then when you set up your optimization criteria in 4nec2, weight the F/B or F/R with 100% and the others with zero (although sometimes, you may want to weight forward gain at 10%, just to keep it from driving to zero gain) |
4nec2 hidden variables.
On 8/14/2011 11:53 PM, Helmut Wabnig wrote:
When optimizing for F/B also 4nec2 results in a too short driven element, same as YAGICAD, they obviously use the same formula, (a long two-liner) from literature. Unlikely... 4nec2 is just driving the finite element NEC engine underneath. YagiCad uses analytical approximations. NEC is *very* sensitive to segmentation, spacing, and wire diameters, etc. particularly when close together or angled. The NEC4 engine is quite a bit better, but you're probably using the default free NEC2 engine. To effectively use this kind of thing, you need to be pretty aware of the limitations and peculiarities of the underlying FEM codes. While I wouldn't expect someone to have read the theory manual for NEC2, you might want to check out some of L.B.Cebik's writeups on using MoM codes, or the stuff in the ARRL Antenna Compendium from time to time. I actually built antennas following that prescription, and they do not work without additional corrections, e.g. a very long hair-pin match. Imagine a 3 element 2 meter yagi, | | | | | | | | | | | | | | | | | | | | | Something is wrong here with the capacitive driven element. Depends on what you were optimizing for. If all you said was "drive F/B to maximum", then it won't try to get you a decent match, all it will do is drive to having element currents that optimize for F/B, which will almost certainly have an evil feedpoint impedance. Now I am having a hard time, because I want to find out in what differs a gain optimized vs a F/B optimized antenna and it is questionable whether that can be done with software. Have not tried other programs yet. What I do is not try to use the optimizer to design the whole antenna including matching network. I optimize the basic element design first (without matching network). Then I add the matching network, hold the element spacing and length constant, and let that optimize. Then I go back and allow element length to change, but hold matching network dimensions/component values (I tend to use lumped element matching networks) fixed. It's an iterative thing because it's tough to specify an appropriate optimization cost function with a simple interface. What you really want is something like "optimize F/B, but keep the feedpoint impedance 20 ohms and 100 reactive ohms" A Yagi with fixed element positions can only be used for 1 frequency (within a very small range) and therefore may be impractical in many situations. The CEBIK tape measure antenna with their water-pipe construction could be easily modified with a moveable center element. this is just not true (otherwise the SteppIR wouldn't work.. it has fixed element spacing and works over a huge (1 octave) frequency range) with fairly good performance. One can also do similar with fixed spacing, and fixed length, and reactive loading of the elements at the centers. |
4nec2 hidden variables.
On Mon, 15 Aug 2011 08:53:35 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: http://imageshack.us/photo/my-images/837/snc14096a.jpg/ Cute cat. However the antenna seems a bit odd. The high carbon steel tape measure elements are not the best for RF conductivity. Good enough for receive, but I would check for RF heating in transmit. The tape measure is also not a circular rod element. You probably modeled it using a circular cross section. That's probably a good first try, but if you want accuracy, the actual element cross section will be needed. That's what I had to do with this stamped sheet metal antenna: http://802.11junk.com/jeffl/antennas/mfj1800/ (Without the hair pin match) http://img5.imageshack.us/img5/3479/snc14112hairpin.jpg Therefore I put the driver on a slider http://img841.imageshack.us/img841/8...14097small.jpg I presume the hairpin match goes between the wing nuts. Looking at the photo of the hairpin, it seems small for matching a simple 2m yagi. It's also a good idea to add a balun and to ground the center of the hairpin match to the center boom. http://vk1od.net/antenna/misc/BetaMatch.htm -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
On Mon, 15 Aug 2011 18:30:05 +0100, Jeff wrote:
Firstly it is not 'drag, drop& move'; it is click, drag& drop! Try reading the Help a little more closely, you will find that it says: "The next thing to do is add a voltage-source. While still in Add-mode, click the 'Source button' (right of the 'Wire button'). Next click and hold down your left mouse-button somewhere in the picture-box. At the current mouse-pointer position a new source-object is displayed. Drag the source-object to the middle of the second wire, just between the two lower wires-ends of the feedline and release the mouse-button. When properly positioned a new source is now added." It does not work as described, when inserting a source on a dipole wire in the center segment, one of the first things to do in Example1. w. Utter Rubbish!!! It works EXACTLY as described!!! Hold down the left mouse button, drag the source to the segment where you wish it to be, release the button - exactly as described!!! Activate the source & add button, then click on the middle segment and expect the source symbol to appear there. It appears but vanishes in an instant leaving a highlighted segment. If the sideways motion is not performed, you do not get it. You have to pull it and that is counterintuitive. The above description may be correct in that you have to pull the object. After having worked with dozens of CAD programs I did not expect such a trap. Many users claim similar difficulties, the internet is full of them. Honestly, who reads all the help files, hundreds of pages? I know there are people who think every bug is a feature. Those people do not live from their own work, somebody else must pay for their living. It took me 3 days to learn 4nec2 because of a long list of "features" including data loss and program crashes. "Notify the author" it suddenly says. The user sits there "What did I do wrong?" which is a nagging question actually when the fault lies elsewhere. All that counts is WALL CLOCK TIME. But it's free. w. |
4nec2 hidden variables.
Utter Rubbish!!! It works EXACTLY as described!!! Hold down the left mouse button, drag the source to the segment where you wish it to be, release the button - exactly as described!!! Activate the source& add button, then click on the middle segment and expect the source symbol to appear there. It appears but vanishes in an instant leaving a highlighted segment. If the sideways motion is not performed, you do not get it. You have to pull it and that is counterintuitive. The above description may be correct in that you have to pull the object. After having worked with dozens of CAD programs I did not expect such a trap. Many users claim similar difficulties, the internet is full of them. Honestly, who reads all the help files, hundreds of pages? I know there are people who think every bug is a feature. Those people do not live from their own work, somebody else must pay for their living. .. Well if you don't actually follow the instructions on the Help then what can you expect! Don't blame the program and then say the Help is wrong or not there! RTFM. "click and hold down your left mouse-button somewhere in the picture-box" then "Drag the source-object to the middle of the second wire". Jeff |
4nec2 hidden variables.
On Mon, 15 Aug 2011 15:09:52 -0700, Jim Lux
wrote: ............. A Yagi with fixed element positions can only be used for 1 frequency (within a very small range) and therefore may be impractical in many situations. The CEBIK tape measure antenna with their water-pipe construction could be easily modified with a moveable center element. this is just not true (otherwise the SteppIR wouldn't work.. it has fixed element spacing and works over a huge (1 octave) frequency range) with fairly good performance. One can also do similar with fixed spacing, and fixed length, and reactive loading of the elements at the centers. In theory ( from the simulations) the Yagi is rather narrowband. Especially the F/B ratio is very frequency dependend. The SteppIr does vary the elements, if I understand it correctly? For practical reasons they do not change element positions on the boom but sufficiently adapt to each frequency band. For the same practical reasons I do it the other way round, move the driver element in the 3 element yagi, and leave everything else as is. This is intended for mobile direction finding. Based on the Cebik pages and improved by making it tuneable by moving the driver along the boom. There is a story behind. ARDF is a sporting endeavour, where people run around in a restricted area searching for a defined signal, or several foxes, as they are called. The antennas are optimized for the fox frequencies. That's child play compared to real world. One night I got a phone call from a desperate guy in Bosnia. They had held a model flight competition there, class F1C, and his model airplane flew ten kilometers away. They put crash transmitters on the models and they range in frequency from 140 to 160 Mhz without any approved frequency raster, just what they can get and not to disturb the neighbour model transmitter. So they need equipment for a 20 MHz range. Most of them use amateur radio handhelds. The transmitters weigh about 5 grams. The Yugoslavian Balkan war was just over, where the killed 200000 people by shooting and cutting throats, and the mine fields were still active and most of them still are today. They put fences around and automatic siren warnings. That desperate guy's model airplane was in or near such an area and night doomed. He has searched for the whole day , was exhausted and could not locate it. "Signals from everywhere and from all directions", he said. That model was his only one for the competition and very expensive, they cost a few thousand dollars. "Signals from everywhere and from all directions." That is a very interesting statement. Did you ever experience such a situation? I had to place foxes and go after them to find out what the problem was which the guy described. I expected an easy job, because I am such an old fart in radio engineering. It was late summer and corn standing two meters high, railway routes nearby, high voltage lines criscrossing the landscape, buildings, hills, mountains, fences, and now imagine it's getting dark and you are in a foreign country where you never had been before, between lakes, rivers, wet ditches and waste water canals. I never knew that 2 or 3 meter high corn fields act as an antenna array. The power lines and railways are wave ducts of extraordinary quality, every metal fence collects and reflects and adds to the reflections from the rocky mountains. Electromagnetic interference overlays the fox signal until you only hear noise and crackles. There you go. I hope the reader can imagine what is the difference to a well planned amateur sport radio fox hunting event. Quickly I recognized that a fixed-frequency ARDF antenna is not suited for the task and one must be able to tune the F/B ratio for the different frequencies the transmitters use, in combination with a conventional attenuator. If your antenna receives from the back, you will hear "signals from all directions". w. |
4nec2 hidden variables.
On Mon, 15 Aug 2011 23:14:19 -0700, Jeff Liebermann
wrote: On Mon, 15 Aug 2011 08:53:35 +0200, Helmut Wabnig [email protected] --- -.dotat wrote: http://imageshack.us/photo/my-images/837/snc14096a.jpg/ Cute cat. However the antenna seems a bit odd. The high carbon steel tape measure elements are not the best for RF conductivity. Good enough for receive, but I would check for RF heating in transmit. The tape measure is also not a circular rod element. You probably modeled it using a circular cross section. That's probably a good first try, but if you want accuracy, the actual element cross section will be needed. That's what I had to do with this stamped sheet metal antenna: http://802.11junk.com/jeffl/antennas/mfj1800/ (Without the hair pin match) http://img5.imageshack.us/img5/3479/snc14112hairpin.jpg Therefore I put the driver on a slider http://img841.imageshack.us/img841/8...14097small.jpg I presume the hairpin match goes between the wing nuts. Looking at the photo of the hairpin, it seems small for matching a simple 2m yagi. It's also a good idea to add a balun and to ground the center of the hairpin match to the center boom. http://vk1od.net/antenna/misc/BetaMatch.htm Thank you for the links, appreciate your help. I fear that in the end I will have to cut and tweak using the antenna analyzer, and with the time perhaps find "tape measure correction factors". Want to keep the design as simple as possible, and hope it works without a balun or additional tricks. Am not yet sure if it will work that way, or not. w. |
4nec2 hidden variables.
On Tue, 16 Aug 2011 09:48:00 +0100, Jeff wrote:
Well if you don't actually follow the instructions on the Help then what can you expect! Don't blame the program and then say the Help is wrong or not there! RTFM. "click and hold down your left mouse-button somewhere in the picture-box" then "Drag the source-object to the middle of the second wire". Jeff Of course you are right, but there are thousands of (unread) help pages left. Should I read them all? On YOUTUBE another (not me) user said, he falls asleep after 4 pages of help text ( the getting started stuff). I printed the "getting started" but fell asleep after page 3. w. |
4nec2 hidden variables.
On 16/08/2011 10:25, Helmut Wabnig wrote:
On Tue, 16 Aug 2011 09:48:00 +0100, wrote: Well if you don't actually follow the instructions on the Help then what can you expect! Don't blame the program and then say the Help is wrong or not there! RTFM. "click and hold down your left mouse-button somewhere in the picture-box" then "Drag the source-object to the middle of the second wire". Jeff Of course you are right, but there are thousands of (unread) help pages left. Should I read them all? On YOUTUBE another (not me) user said, he falls asleep after 4 pages of help text ( the getting started stuff). I printed the "getting started" but fell asleep after page 3. w. Well since the instructions on how to add a source are on page one, it would appear that you went to sleep earlier than you thought!! Just because a program does not work the way that YOU expect, or perhaps would like, does not warrant the out and out rant that you started this thread with. All of the information on how to run the program was actually there if you had bothered to read it rather than wasting time complaining about nothing. Jeff |
4nec2 hidden variables.
On 8/16/2011 2:25 AM, Helmut Wabnig wrote:
On Tue, 16 Aug 2011 09:48:00 +0100, wrote: Well if you don't actually follow the instructions on the Help then what can you expect! Don't blame the program and then say the Help is wrong or not there! RTFM. "click and hold down your left mouse-button somewhere in the picture-box" then "Drag the source-object to the middle of the second wire". Jeff Of course you are right, but there are thousands of (unread) help pages left. Should I read them all? On YOUTUBE another (not me) user said, he falls asleep after 4 pages of help text ( the getting started stuff). I printed the "getting started" but fell asleep after page 3. w. Should you read them? Depends on if you want to make use of the program or not. for ANY modeling program (and any drafting program, as well) there's a fairly big first step in the learning curve. And, because 4nec2 isn't a "drafting" or "drawing" program, it's UI doesn't follow the more common conventions. It's designed to make entering antennas easy for some subset of people. 4nec2 started with just using notepad to edit the NEC input deck and a formatted editor to edit cards. Folks who start with EZNEC often find using raw NEC decks difficult, because they're used to the tabular model entry of EZNEC. Folks who start with Visio, pre version 5, find modern versions of Visio a pain, because the UI changed to conform to PowerPoint. Autocad is certainly not "intuitive" unless you've been using it a while. For what it's worth, the 4nec2 help files are a whole lot better than the documentation for NEC itself. Beyond the details of entering the geometry and simulation conditions (which are idiosyncratic for ALL antenna modeling programs.. no two are alike, nor are the input file formats directly compatible, for the most part) There's a fair amount of "art" in effectively using the programs and understanding the limitations inherent in the modeling technique being used (method of moments on wires for NEC). It's not just a matter of creating a bazillion segments and letting your processor grind away, because there's all sorts of subtle numerical precision issues. 4nec2 (and EZNEC) both provide some amount of help in keeping you away from egregious model errors (segment lengths that are unreasonable relative to wavelength and/or wire diameter). There's also well known techniques for modeling flat surfaces with meshes that provide results that match actual measurement, even if the model doesn't "look" quite right if you render it. NEC is very much a power tool like a chainsaw.. you can do things that you couldn't do with hand tools, but you can also do things that you don't really want. It takes some practice and background knowledge to use it effectively. The value of purpose built modeling tools like AO is that they have a very constrained model space tuned to a particular application, so the program can a) have a simple model entry (e.g. you can only do Yagi-Uda) b) have a sophisticated objective function for optimization NEC is a lot harder: you can enter any geometry from a simple wire to an entire battleship with 100s of antennas. |
4nec2 hidden variables.
On Tue, 16 Aug 2011 11:21:20 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: Thank you for the links, appreciate your help. Y'er welcome. However, I still don't have a clue what you're trying to accomplish. If you want super front to back ratio for a direction finding antenna, you need a wall, not a phased single wire reflector as in a yagi. Something like a dish or a panel reflector will work, but is probably not practical. As you discovered, the position of the reflector is very critical for maintaining the best F/B ratio. It's also very sensitive to frequency. You might be able to make it work with a flimsy tape measure, but it probably won't be very stable in the field. Permit me to offer another idea. Instead of direction finding by the peak signal, do it with a null. Two identical dipoles, a T connector, and some coax, are all that are required. Space them about 1/4 wavelength apart. Insert a 3/4 wave coax phasing section between the two dipoles. Signals from the front antenna will cancel when they reach the 2nd antenna yielding a cardioid pattern. It will be just as critical and sensitive to frequency and position as your yagi, but methinks will work better. I've obtained 50dB deep nulls with this method. The good news is that you really only need one adjustment on the antenna, which is the relative distance between dipoles, which is easily accomplished by sliding the antenna on the boom. The adjustment range is limited, so an assortment of coax phasing lengths will also be needed. Adjusting the antenna for best null at a specific frequency, prior to transmitter hunting, is a necessary complication. I also use this method on my home base station to null out a rather strong repeater, so I can talk to a distant repeater on the same frequency. I've also built one using 4 identical rubber ducky antennas for 2meters. It sorta worked but I could only get a 10dB deep null. Both EZNEC and 4NEC have HF examples of this type of antenna. cardioid.ez and \models\HFvertical\cardioid.nec I fear that in the end I will have to cut and tweak using the antenna analyzer, and with the time perhaps find "tape measure correction factors". More bad news. You really do have to TEST your creations to see if the simulations and models are correct. I tend to make far too many simplifying assumptions in my models, which show up as errors in the actual construction. Want to keep the design as simple as possible, Simple is good. Crude is not. Recognizing the difference is difficult. and hope it works without a balun or additional tricks. Am not yet sure if it will work that way, or not. It won't work well without a balun. The coax will radiate, giving unpredictable directional indications. You can minimize the effects with ferrite beads, a sleeve balun, or with just a coax loop. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
On Tue, 16 Aug 2011 11:14:24 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: The SteppIr does vary the elements, if I understand it correctly? For practical reasons they do not change element positions on the boom but sufficiently adapt to each frequency band. Perhaps reading the Steppir patent might be illuminating: http://www.google.com/patents?id=rw6xAAAAEBAJ Note that the elements do not change position, only their length. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
On 8/16/2011 9:25 AM, Jeff Liebermann wrote:
On Tue, 16 Aug 2011 11:21:20 +0200, Helmut [email protected] --- -.dotat wrote: Thank you for the links, appreciate your help. Y'er welcome. However, I still don't have a clue what you're trying to accomplish. If you want super front to back ratio for a direction finding antenna, you need a wall, not a phased single wire reflector as in a yagi. Something like a dish or a panel reflector will work, but is probably not practical. As you discovered, the position of the reflector is very critical for maintaining the best F/B ratio. It's also very sensitive to frequency. You might be able to make it work with a flimsy tape measure, but it probably won't be very stable in the field. Permit me to offer another idea. Instead of direction finding by the peak signal, do it with a null. Exactly.. you can get very sharp nulls pretty easily. For simple antennas, there's usually an ambiguity, but you can resolve that by other means. |
4nec2 hidden variables.
On Tue, 16 Aug 2011 11:14:24 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote: "Signals from everywhere and from all directions." Hi Helmut, The signal is too STRONG. I'm surprised you have not recognized this common fox hunting problem. There needs to be an attenuator between the antenna and the receiver. 73's Richard Clark, KB7QHC |
4nec2 hidden variables.
On Tue, 16 Aug 2011 09:51:53 -0700, Jim Lux
wrote: On 8/16/2011 9:25 AM, Jeff Liebermann wrote: Permit me to offer another idea. Instead of direction finding by the peak signal, do it with a null. Exactly.. you can get very sharp nulls pretty easily. For simple antennas, there's usually an ambiguity, but you can resolve that by other means. With the cardioid pattern, there's no ambiguity. With a deep null, and a non-reflective environment, it's easy to use. However, reflections off buildings and hills are a problem. The antenna is roughly an omnidirectional antenna, and reflections will appear to fill in the deep null. Not much can be done about that except to move and try a different location. My favored method is by using a map. Find a position, determine a bearing, and draw a line of position on the map. Then, find a different location, and do it again. Repeat as often as practical generating as many LOP's as possible. Some of the LOP's will be totally insane, but a majority should cross at one point on the map. (This has been automated in software, but a map is good enough). In 1976, I helped design the AN/SRD-21 homer DF, which DOES have a 180 degree ambiguity. http://802.11junk.com/jeffl/AN-SRD-21/ If the homing receiver works in the same manner as described in the above manual (PIN antenna switch, synchronous demodulator, charge pump, and zero center meter), resolving the ambiguity is easy. Just rotate the homing antenna to the right. If the zero center meter indicates that you should turn back to the left, then you have the correct direction. If it indicates that you should continue to turn to the right, then you have the wrong direction. This has nothing to do with the topic at hand, but I thought it might be of interest. Some of my ancient comments on Doppler direction finding: http://www.qsl.net/n9zia/doppler_notes1.txt http://www.qsl.net/n9zia/doppler_notes2.txt -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
4nec2 hidden variables.
In article ,
Jeff Liebermann wrote: With the cardioid pattern, there's no ambiguity. With a deep null, and a non-reflective environment, it's easy to use. However, reflections off buildings and hills are a problem. The antenna is roughly an omnidirectional antenna, and reflections will appear to fill in the deep null. Not much can be done about that except to move and try a different location. My favored method is by using a map. Find a position, determine a bearing, and draw a line of position on the map. Then, find a different location, and do it again. Repeat as often as practical generating as many LOP's as possible. I have seen recommendations that one do this by proceeding in a straight line, taking bearings at positions of around 1/4 wavelength or so. The effects of multipath will tend to cause the measured bearing to wobble back and forth across an arc (as you go down the line) and the true bearing will tend to be close to the center of that arc. I haven't tried this approach myself... but it might combine well with your "take readings from lots of different locations" approach, by helping cancel out some of the effects of multipath. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
4nec2 hidden variables.
On 8/16/2011 3:16 PM, Dave Platt wrote:
In , Jeff wrote: With the cardioid pattern, there's no ambiguity. With a deep null, and a non-reflective environment, it's easy to use. However, reflections off buildings and hills are a problem. The antenna is roughly an omnidirectional antenna, and reflections will appear to fill in the deep null. Not much can be done about that except to move and try a different location. My favored method is by using a map. Find a position, determine a bearing, and draw a line of position on the map. Then, find a different location, and do it again. Repeat as often as practical generating as many LOP's as possible. I have seen recommendations that one do this by proceeding in a straight line, taking bearings at positions of around 1/4 wavelength or so. The effects of multipath will tend to cause the measured bearing to wobble back and forth across an arc (as you go down the line) and the true bearing will tend to be close to the center of that arc. I haven't tried this approach myself... but it might combine well with your "take readings from lots of different locations" approach, by helping cancel out some of the effects of multipath. There's a photograph of this technique on a field with little flags at different distances all oscillating around a single line illustrating it in some ARRL publication (probably an antenna compendium, but maybe the handbook or antenna book). |
4nec2 hidden variables.
On Tue, 16 Aug 2011 17:13:15 -0700, Jim Lux
wrote: On 8/16/2011 3:16 PM, Dave Platt wrote: In , Jeff wrote: With the cardioid pattern, there's no ambiguity. With a deep null, and a non-reflective environment, it's easy to use. However, reflections off buildings and hills are a problem. The antenna is roughly an omnidirectional antenna, and reflections will appear to fill in the deep null. Not much can be done about that except to move and try a different location. My favored method is by using a map. Find a position, determine a bearing, and draw a line of position on the map. Then, find a different location, and do it again. Repeat as often as practical generating as many LOP's as possible. I have seen recommendations that one do this by proceeding in a straight line, taking bearings at positions of around 1/4 wavelength or so. The effects of multipath will tend to cause the measured bearing to wobble back and forth across an arc (as you go down the line) and the true bearing will tend to be close to the center of that arc. I haven't tried this approach myself... but it might combine well with your "take readings from lots of different locations" approach, by helping cancel out some of the effects of multipath. There's a photograph of this technique on a field with little flags at different distances all oscillating around a single line illustrating it in some ARRL publication (probably an antenna compendium, but maybe the handbook or antenna book). I think the photo was on interferometry for direction finding, where they were trying to plot the wavefront pattern. I recall the photo, but I couldn't find it in the ARRL Antenna Handbook (19th edition). However, the handbook does have a full chapter on direction finding (Ch 14) which includes the cardioid antenna. The purpose of me using multiple bearings is simply to eliminate the effects of reflections. It's not totally foolproof, but better than chasing a single bearing. There are better ways, but they're usually not very portable. A rotating antenna direction finder can easily distinguish between the incident signal from a reflection. Such direction finders display something like the antenna pattern on a polar display. The incident signal is very steady and does not move in azimuth. Reflections jitter dramatically in both amplitude and azimuth. They also tend to appear and disappear rapidly and erratically. Rotating antenna DF antennas: http://www.rockwellcollins.com/sitecore/content/Data/Products/EW_and_Intelligence/SIGINT/ANT-1040A_Airborne_Spinning_DF_Antenna.aspx http://www.rockwellcollins.com/sitecore/content/Data/Products/EW_and_Intelligence/SIGINT/ANT-1040_Spinning_DF_Antenna.aspx 20 in diameter, 25 in high, 50 lbs. Another method that I've used is to generate a narrow "beam" using two identical yagi antennas that share a common reflector. The antennas are oriented about 20 degrees apart with the reflector at the vertex. A near perfect audible square wave drives two identical PIN diode switches on the driven elements. While the antenna may have a -3dB beamwidth of perhaps 10 degrees, the LOP of equal antenna signal levels is extremely sharp, and often less than 0.5 degrees. A synchronous demodulator, charge pump, differential amp, and zero center meter complete the systems. You can also do it by ear by listening to the null at the switching frequency. If the antennas and PIN diode switches are perfectly symmetical, all boresight error cancel. I originally contrived the system by reading about the Lorenz beam bombing system used by the German's during WWII, but later discovered that others had anticipated the idea. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
direction finding
On 8/16/2011 9:35 PM, Jeff Liebermann wrote:
On Tue, 16 Aug 2011 17:13:15 -0700, Jim wrote: I think the photo was on interferometry for direction finding, where they were trying to plot the wavefront pattern. I recall the photo, but I couldn't find it in the ARRL Antenna Handbook (19th edition). However, the handbook does have a full chapter on direction finding (Ch 14) which includes the cardioid antenna. Could be.. The purpose of me using multiple bearings is simply to eliminate the effects of reflections. It's not totally foolproof, but better than chasing a single bearing. There are better ways, but they're usually not very portable. A rotating antenna direction finder can easily distinguish between the incident signal from a reflection. Such direction finders display something like the antenna pattern on a polar display. The incident signal is very steady and does not move in azimuth. Reflections jitter dramatically in both amplitude and azimuth. They also tend to appear and disappear rapidly and erratically. snip Another method that I've used is to generate a narrow "beam" using two identical yagi antennas that share a common reflector. snip A popular scheme from WJ 30 years ago (at the advent of digital signal processing) used 3 antennas in a triangle, and basically did interferometry. Sampling the data and using an FFT lets you do a wide band at one time (which is handy if you want to DF frequency hopping radios, which became very popular in the 80s) |
direction finding
On 8/17/2011 11:02 AM, Jim Lux wrote:
A popular scheme from WJ 30 years ago (at the advent of digital signal processing) used 3 antennas in a triangle, and basically did interferometry. Sampling the data and using an FFT lets you do a wide band at one time (which is handy if you want to DF frequency hopping radios, which became very popular in the 80s) As far as VHF, I know a couple here in town I've seen using arrays for direction finding. But they used four verticals in a square. It worked quite well. We had one guy that kept jamming one of the repeaters, and the user of said array was easily capable of tracking him down to a shopping center parking lot where the guy was sitting in his car. I suspect the expression on the jammers face when the tracker tapped on his window was priceless. :) The device in the car used an array of LED's in a cross configuration if I remember right. He had the antenna array on the back of his truck. I don't recall the element spacing. |
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